MEMS have been shown to be useful for a variety of consumer, industrial and military applications. Most MEMS devices are fabricated on semiconductor substrates (e.g., silicon, Gallium Arsenide, Silicon-On-Insulator, etc.) using standard Integrated Circuit (IC) processes in combination with specialized micromachining processes. Collectively these manufacturing technologies are frequently called microfabrication processes.
Recently there has been a large interest in making MEMS Radio Frequency (RF) devices and systems for a variety of high volume communication applications. MEMS-based RF components and systems have typically been realized on traditional semiconductor materials, primarily silicon wafers, due to the high quality of the materials and processes developed over the years and due to the expectation of direct monolithic integration of the MEMS with integrated circuits. This approach has several disadvantages for the performance and potential commercialization of RF and microwave devices. In particular, the dielectric losses of the silicon substrate are very high at frequencies above 1 GHz and high metallization sheet resistances. Further, such MEMS components can produce RF interference into underlying and surrounding circuitry and vice versa.
There is also a benefit in producing MEMS variable capacitors that meet certain performance requirements. For example, there is a desire to provide MEMS variable capacitors having high quality factor (Q) over a range of different frequencies. Also, there is a desire to provide MEMS variable capacitors with improved capacitance ratio (the ratio of minimum to maximum capacitance of a variable capacitor). The capacitance ratio may be achieved by providing variable capacitors with a minimized parasitic fixed capacitance and maximized capacitance in the high capacitance state. It is also desired to highly isolate the RF portions of the MEMS circuits from the substrate noise and losses.
In view of the foregoing, it is desired to provide improved MEMS variable capacitors and actuation components and methods.